In general, any member of the mammalian order Primates, with the exception of the tree shrews, the lemurs and their allies, the gibbons and apes, and humans. Monkeys are arranged into two main groups: those of the Old World tropics, the catarrhines, with two families, Cercopithecidae (monkeys with cheek pouches) and Colobidae (leaf monkeys); and those of the New World tropics, the platyrrhines, also with two families, Callitrichidae (marmoset) and Cebidae. Monkeys live in tropical forests, where they move about by using all four limbs. Except ....